Ceramic is a material suitable for heat exchangers because of its light weight compared with metals and good thermal conductance. Particularly because of its good heat resistance, ceramic is regarded as a promising material for use in recovery of heat from high-temperature gases above 800° C., such as exhaust gases from gas turbines or others. Commonly used in high-temperature applications are metallic plate-fin heat exchangers, which exhibit high effectiveness, but have a drawback that complicated fin shapes lead to high costs. Ceramic is, however, a material difficult to work into complicated shapes because of its high hardness and brittleness. Heat exchangers using ceramic having such properties have already proposed, as seen in patent documents 1 to 3, for example.
The ceramic heat exchanger disclosed in patent document 1 is an integrally-fired ceramic product comprising an outer frame and walls defining a plurality of channels inside the frame, intended to force a high-temperature fluid and a low-temperature fluid to flow through the channels in opposite directions to transfer heat from the high-temperature fluid to the low-temperature fluid via the walls.
The ceramic heat exchanger disclosed in patent document 2 is a sintered product produced by forming a plurality of grooved plate-form shapes from a mixture of silicon carbide powder, carbon powder and a binder, then forming a stack of the grooved plate-form shapes by provisionally bonding them with a bonding agent, the stack having minute holes formed of the grooves, then degreasing, or removing the binder from the stack, then heating, then impregnating the stack with molten silicon, and then reaction-sintering the stack.
The ceramic heat exchanger disclosed in patent document 3 comprises a casing for exhaust gases to flow through, and a plurality of tubes fitted to the casing to extend through the opposite end walls of the casing and across the interior of the casing, the tubes being intended to contain and circulate a heat medium in the direction from an exhaust gases outlet side to an exhaust gases inlet side, wherein spaces between the tubes and the end walls of the casing are filled with a liquid-form ceramic material which is matured into a ceramic, or filled with a solid-form ceramic material which is impregnated with a liquid-form ceramic material and matured into a ceramic.